Conventional freight railroad cars in North America and other parts of the world typically include a car body and two spaced apart trucks. The car body or car body under frame typically includes two spaced apart center plates that respectively rest on and are rotatably or swivelly received by bolster bowls of the two trucks. The trucks rollingly support the car body along railroad tracks or rails. Each truck typically has a three piece truck configuration that includes two spaced apart parallel side frames and a bolster. The side frames extend in the same direction as the tracks or rails, and the bolster extends transversely or laterally to the tracks or rails. The bolster extends laterally through and between and is supported by the two spaced apart side frames. Each side frame typically defines a center opening and pedestal jaw openings on each side of the center opening. Each end of each bolster is typically supported by a spring group positioned in the center opening of the side frame and supported by the lower portion of the side frame that defines the center opening.
Each truck also typically includes two axles that support the side frames, four wheels, and four roller bearing assemblies respectively mounted on the ends of the axles. The truck further typically includes four bearing adapters respectively positioned on each roller bearing assembly in the respective pedestal jaw opening below the downwardly facing wall of the side frame that defines the top of the pedestal jaw opening. The wheel sets of the truck are thus received in bearing adapters placed in leading and trailing pedestal jaws in the side frames, so that axles of the wheel sets are generally parallel. The bearing adapters permit relatively slight angular adjustment of the axles. The spring sets permit the side frames to partially move with respect to the bolster, about longitudinal, vertical, and transverse axes.
Directions and orientations herein refer to the normal orientation of a railroad car in use. Thus, unless the context clearly requires otherwise, the “longitudinal” axis or direction is substantially parallel to the tracks or rails and in the direction of movement of the railroad car on the tracks or rails in either direction. The “transverse” or “lateral” axis or direction is in a substantially horizontal plane and is substantially perpendicular to the longitudinal axis and the tracks or rails. The term “inboard” means toward the center of the railroad car, and may mean inboard in a longitudinal direction, a lateral direction, or both. Similarly, “outboard” means away from the center of the railroad car. “Vertical” is the up-and-down direction, and “horizontal” is in a plane parallel to the tracks or rails including the transverse and longitudinal axes. A truck is considered “square” when its wheels are aligned on parallel tracks or rails and the axles are parallel to each other and perpendicular to the side frames. The “leading” side of the truck means the first side of a truck on a railroad car to encounter a turn; and the “trailing” side is opposite the leading side.
Roller bearing adapter assemblies including an adapter shear pad and mating roller bearing adapter have long been known in railroad car trucks for supporting the truck side frames on the wheel sets. Each adapter shear pad generally functions to decouple the wheels and axle from the side frame to improve steering of the truck as further explained below. The adapter shear pads must also provide electrical continuity or conductivity between the side frame and the roller bearing adapter (and thus between the car body and the tracks or rails). The electrical continuity or conductivity is needed to ground the car body to eliminate or reduce the buildup of static electricity on the car body. The electrical continuity or conductivity is also needed for the car body or components thereof (such as electric solenoids for doors on bottom dump freight railroad cars) to obtain electrical power or electrical signals from the railroad tracks or rails. In other words, this electric continuity or conductivity is needed to provide electric power or electric signals transmitted from the tracks or rails to one or more components of the car body. The electrical continuity or conductivity is further needed to provide electrical continuity or conductivity between railroad cars to trigger railroad crossing signals.
Such roller bearing adapter assemblies in the past included adapters using metal wear liners that permitted limited lateral and longitudinal movement of the side frames relative to the roller bearing adapters positioned on the wheel sets under loaded car due to high frictional resistance.
Subsequently, elastomeric mountings took the place of the metal wear liners to provide controlled flexibility in all directions, particularly for passive-steering rail car trucks.
For instance, U.S. Pat. No. 7,387,074 discloses a roller bearing adapter and a partially elastomeric adapter shear pad. This roller bearing adapter is configured to fit on top of the roller bearing and this adapter shear pad is configured to fit on top of the roller bearing adapter. The adapter shear pad is made from an elastomer such as polyurethane.
In another example, U.S. Pat. No. 7,739,961 discloses an improved elastomeric mounting that reduces the thickness from over 1 inch to ½ inch. U.S. Pat. No. 7,739,961 discloses that the adapter shear pad shear stiffness decreases under higher vertical and longitudinal loads.
These and other known roller bearing adapters and adapter shear pads do not fully address the ever increasing and expected future demands for freight car truck performance in the railroad industry. More specifically, while the various current known and commercially available three piece truck configurations with primary suspension pads meet current Association of American Railroads (“AAR”) specifications, enhanced specifications are being developed by the AAR and it is expected that the current three piece truck configurations may not meet these new AAR specifications. These AAR enhanced specifications set forth or codify the continuing and ongoing demands in the railroad industry for improved freight car truck performance to: (a) reduce wheel wear and damage; (b) reduce rolling resistance; (c) reduce fuel consumption; (d) reduce the need for and thus cost of railroad track repair (including reducing the cost of rail and tie maintenance); (e) reduce truck hunting and improve high speed stability (“HSS”) for both empty and loaded railroad cars; and (f) improve curving performance for both empty and loaded railroad cars.
For example, certain known trucks in certain instances may become less stable under a loaded car in shallow curves (such as a 1 degree curve) or while encountering certain rail perturbations.
In other examples, certain known trucks do not provide optimum curving performance, and more specifically, certain known trucks do not enable the axles to optimally align with high degree curves.
More specifically, on straight track or straight rails, a three piece truck with parallel side frames and parallel wheel set axles perpendicular to the side frames (i.e., a substantially perfectly “square” truck) rolls without inducing lateral or transverse forces between the wheel flange and the rail. However, at higher speeds, even minor imperfections or perturbations in the tracks or rails or in the equipment can lead to a condition known as “hunting” that refers to a yawing or oscillating lateral movement of the wheel sets along the rails that causes the railroad car to move side-to-side on the rails. More than minor imperfections or perturbations in the tracks or rails or in the equipment can lead to greater truck hunting even at lower speeds. On trucks with insufficient rigidity, this results in a condition variously known as “warping,” “parallelogramming,” or “lozenging,” wherein the side frames remain parallel, but one side frame moves forward with respect to the other side frame. Trucks with insufficient rigidity can permit hunting. Hunting tends to increase wheel wear and damage, increase fuel consumption, increase the need for railroad track repair, and decrease HSS. In certain instances, hunting has also led to derailments, damage to the lading, and damage to the freight railroad cars.
Curved railroad track or rails poses a different set of challenges for the standard three-piece truck. When a railroad car truck encounters a curve or turn, the distance traversed by the wheels on the outside of the curve is greater than the distance traversed by wheels on the inside of the curve, resulting in lateral and longitudinal forces between the respective wheels and rails. On trucks with insufficient rigidity, they can warp increasing the wheel set angle-of-attack relative to the tracks or rails causing undesirable lateral forces. These wheel forces often cause the wheel set to turn in a direction opposing the curve or turn.
Various current railroad car repair billing indicates that over fifty percent of removals of freight railroad cars from service for repair are related to wheel sets. A majority of these wheel set removals are due to wheel tread damage primarily caused by wear and rolling contact fatigue. In certain instances, surface cracks can form in the tread from large creep forces generated from a wheel set with a high angle of attack. In certain instances, the flanges of the wheels also wear due to inadequate truck steering and/or hunting.
To improve curving performance, it is known to interpose an elastomeric bearing member between the side frame and the tops of the bearing adapters. The elastomeric member: (a) provides, on curved tracks or rails, the wheel sets a limited amount of freedom of movement to depart from a square relationship to respond to turning forces and accommodate the nonparallel condition of the axles (b) provides forces to aid the wheelset to return to a parallel state after the curve and on straight track. The elasticity of the elastomeric bearing member biases the wheel set to return to its square position. To provide the standard three piece truck with the ability to negotiate turns with less rolling resistance, certain known trucks are generally configured to enable a nonparallel condition of the axles during the curve or turn, that is then recovered on the straight tracks or rails. This may be achieved by permitting relative movement of the bearing adapters within the pedestal jaws of the side frames.
It should thus be appreciated that: (a) there are typically competing performance demands for better curving and less truck hunting; (b) many of the truck improvements that facilitate better curving allow more truck hunting; and (c) many of the truck improvements that reduce truck hunting reduce the curving performance. It should also be appreciated that known and proposed three piece trucks are limited in their curving and high speed stability performance.
Accordingly, there is a need to meet these ongoing demands in the railroad industry for improved freight car truck performance, and more specifically to provide a truck that provides better curving while simultaneously reducing truck hunting.